EP-0 686 491 B1 describes a method for manufacturing contact lenses with the aid of cast molding. In the publication it is described that a cast mold is manufactured with the aid of injection molding. The known apparatus is rather complicated and hence costly. While in the known apparatus cast molds provided with a cup bottom part and a cup top part are formed, these parts are not provided with special provisions allowing them to be clamped onto each other. As a result of the lack of such clamping means, during hardening of the monomeric material introduced into the cup bottom part for forming a contact lens, the top part has to be continuously pressed onto the cup bottom part with an external press-on device especially provided for that purpose. This leads to a relatively costly apparatus. Further, a part of the manufacturing process is to take place under vacuum, which also adversely affects the costs of the total system to a considerable extent.